The proposed research will investigate neural and neurochemical mechanisms regulating the release of pituitary hormones. The experiments will involve electrical stimulation of the brain of sheep concurrent with repeated sampling of blood for hormone quantification. Ovarian and other hormones known to have feedback effects on release of pituitary hormones will also be administered. Monoamines suspected of being synaptic transmittors in the neural control of pituitary hormone release will be studied as well.